1. Field of the Invention
This invention relates to a process for producing a fiber comprising a gel, particularly to a process for producing a fiber comprising a gel having the property of reversibly swelling and shrinking by an external action.
2. Related Background Art
A process for producing a synthetic fiber generally includes the spinning step of forming a polymer as the source material into a state readily flowable according to the method suitable for its physical properties, namely dissolving the polymer in an appropriate solvent to prepare a solution or melting the polymer into a molten state and extruding the solution or the melt through a nozzle with a predetermined size to solidify it into a fiber and the finishing step corresponding to various requirements for improvement of the physical properties of the fiber obtained.
As the spinning method when using a solution of a polymer as the dope for spinning, there are the wet spinning method and the dry spinning method.
The wet spinning method is a method for obtaining a polymer fiber by spinning out, namely extruding through a spinneret for spinning a solution of a polymer for formation of fiber (dope for spinning) into a solution for coagulation of said polymer, elongating the discharged liquid stream to a filament with a desired thickness and collecting the filament by means of a mechanical device such as rotatory bobbin, centrifugal device, etc. Fibers such as vinylon or acrylic fibers are produced according to this method.
For example, in production of vinylon using polyvinyl alcohol which is a water-soluble polymer as the source material, an aqueous PVA solution with a concentration of about 15% is used as the dope for spinning, while an aqueous solution of a salt such as Glauber's salt, ammonium sulfate, etc., or an alkali such as sodium hydroxide, etc., is used as the liquid for coagulation of the polymer.
On the other hand, the dry spinning method is a method in which the dope for spinning is extruded through a spinneret for spinning into a heated gas to solidify the polymer by evaporation of the solvent in the dope for spinning. Vinylon, acrylic fibers, vinyl chloride fibers, etc., have been produced according to this method.
For example, in production of vinylon according to the dry spinning method, an aqueous PVA solution with a high concentration of about 30 to 50% is used as the dope for spinning and the solution is spun into heated gas.
When the desired physical properties cannot be satisfactorily obtained in the fiber formed by the spinning step, the step for improving the physical properties of the fiber is further practiced if desired.
For example, in production of vinylon as mentioned above, the heat treatment step and the acetalization step are conducted after the spinning step.
In the heat treatment step practiced here, the fiber is heated in air of 210.degree. to 220.degree. C., whereby crystallization of the fiber progresses to impart primarily water resistance and strength to the fiber. On the other hand, in the acetalation step, the fiber subjected to the above heat treatment step is treated by dipping in an aqueous solution containing formaldhyde, sodium sulfate and sulfuric acid at prescribed concentrations, optionally under heating. By this treatment, hydrophilic hydroxyl groups in the polymer are crosslinked with each other to make the fiber resistant to hot water.
The synthetic fibers produced according to the methods as described above have been utilized primarily as fibers for clothing, or as fibers for industrial use such as ropes, tires, various fillers, etc., and these fibers are generally demanded to have sufficient tensile strength and water resistance, or adequate stretchability and uniformness in shape. Accordingly, for satisfying these requirements, the post-treatment after spinning such as heat treatment and acetalization treatment in production of vinylon as described above has been practiced.
The present inventors have made various investigations about production of a novel fiber having characteristics and functions not obtained in the fibers of the prior art as described above, and consequently found that a fiber having physical properties and functions not obtained in the fibers of the prior art can be provided by obtaining a fiber comprising a gel to accomplish the present invention.